Controlling temperature of nitration reactions



Patented Dec. 13, 1938 UNT STTS CONTROLLING TEMPERATURE or NITRA- TION REACTIONS Philip G. Wrightsman,

Chester, Pa., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 1, 1934, Serial No. 755,585

5 Claims.

This invention relates to a process of carrying out exothermic chemical reactions, and more particularly to a process for controlling the temperature in such reactions.

In chemical operations it is frequently necessary to remove the heat generated in the reaction by some suitable cooling means. While this is frequently achieved in small scale laboratory preparations by means of external cooling of the reaction chamber, in large scale operations it is more generally the practice to circulate cold brine or similar media through coils suspended in the reaction mixture. Although this is ordinarily satisfactory, in the manufacture of explosive substances such as nitroglycerin the use of brine or similar cooling media involves considerable hazard, since the influx of brine into the reaction mixture through small leaks is likely to cause local overheating and consequent explosive decomposition. Because of this danger, it is the common practice to test the cooling coils frequently for leaks and to change the entire cooling system after a certain number of runs. This practice is disadvantageous and expensive in all cases, but, in the more complicated cooling systems such as those employed in certain continuous nitration processes containing a great number of joints Within the nitrator, this procedure is a costly and altogether inadequate B safety precaution.

I'he purpose of this invention is to control the reaction temperatures in exothermic chemical reactions, especially when compounds are formed that tend to decompose at elevated temperatures. A further object is to minimize the danger of explosive decomposition in the production of nitrated organic compounds. A still further object is to prevent the contamination of finished materials by foreign substances introduced inad- 10 vertently into the containing vessel. Other ob- "ects will appear hereinafter, as the invention is further disclosed.

The foregoing objects are accomplished by my new and improved process for controlling the reaction temperature which consists in maintaining in heat exchange relationship with the reaction mixture a cooling medium comprising at least one of the non-aqueous, non-saline substances present in the reaction mixture.

In accordance with one embodiment of my invention, the brine employed in the cooling system of a nitroglycerin nitrator is replaced by socalled mixed acid such as that employed in the reaction chamber. This mixed acid consists approximately of 54 parts of sulfuric acid and 46 parts of nitric acid which is cooled to the desired low temperature. Any mixture, however, containing from 30 to 70% sulfuric acid and from 50 to 20% nitric is satisfactory. A mixed acid within these limits will not congeal at a temperature well below 0 C., and it may therefore be employed directly in the cooling coils of the system in place of the usual saline media. Since the cooling coils are made to withstand the corrosive action of the substances in the reaction chamber, no changes in equipment are necessary in order to employ one or more of these substances within the cooling system. A preferred embodiment of my invention comprises an acid composition of the approximate composition 55% H2304, 30% HNOs, and-l% H2O. This composition is sufliciently low freezing and in many instances would be more preferable than the customary nitroglycerin mixed acid from the standpoint of viscosity.

Similar processes for controlling the reaction temperature may be employed in the manufacture of trinitrophenyl-methylnitramine, or tetryl. A cooling medium consisting, for example, of parts of sulfuric acid, 80 parts of nitric acid, and 10 parts of Water may be circulated through the cooling coils in the tetryl or like nitrator, this being approximately the composition of the mixed acid employed in the conversion of dimethyl aniline to tetryl.

A further application of my invention is in the preparation of nitrobenzene. In such a process the cooling medium circulating through the cooling coils may be either nitrobenzene, the product of the reaction, or the mixture of sulfuric and nitric acids employed in the nitration, or even benzene itself. Any one of these compounds may serve, since no material foreign to the reaction is introduced.

While a mixed acid of widely varying composition may be employed, the maximum of protection against the results of leaks in the cooling system will, of course, be afforded by the use of a mixed acid of a similar composition in both the nitration reaction and the cooling system. In general, however, my invention is applicable to controlling the temperature of any reaction in which the accidental contamination of the reaction mixture or product by the cooling medium is dangerous or otherwise objectionable. It is only necessary to substitute for the saline medium one or more of the non-aqueous substances present in the reaction mixture, such that the desired cooling medium will be a non-corrosive liquid at the temperature, and in the equipment,

employed. For example, other acids may be used, such as nitric, sulfuric, or even phosphoric.

The advantages of the invention are outstanding in the manufacture of nitroglycerin, where a small undetected leak in the cooling system might result in a dangerous decomposition, if brine or similar medium were employed. If, in accordance with my invention, a mixed acid is used, this hazard is entirely avoided. It no longer becomes necessary to drown the charge and shut down the plant when a leak is discovered. Thus there results not only greater economy of operation, but increased safety and the avoidance of loss of time and equipment resulting from disastrous explosions. In addition to these advantages, a product is obtained which has not been inadvertently contaminated by the cooling medium during manufacture.

By the term foreign reaction as used herein is intended any reaction other than the reaction or reactions occurring in the processes being carried out.

Many variations in detail from the procedure described above may be made without departing from the spirit of the invention. I intend, therefore, to be limited only as indicated in the following patent claims.

I claim:

1. The process for controlling the reaction temperature in the nitration of organic compounds to produce an explosive, which comprises maintaining the reaction mixture in direct heat exchange relationship with a single liquid cooling medium taken from the group consisting 2. The process for controlling the reaction terriperature in the production of nitroglycerin which comprises maintaining the reaction mixture in direct heat exchange relationship with a single cooling medium containing from 30-70% sulfuric acid and from 50-30% nitric acid, said cooling medium being out of direct contact with said reaction mixture.

3. The process for controlling the reaction temperature in the nitration process for the production of aliphatic nitric esters, which comprises maintaining the reaction mixture in direct heat exchange relationship with a single cooling medium consisting of sulfuric and nitric acids, said cooling medium being out of direct contact with said reaction mixture.

4. The process fon controlling the reaction temperature in the nitration process for the production of nitroglycerin, which comprises maintaining the reaction mixture in direct heat exchange relationship with a single cooling medium consisting of a mixture of sulfuric and nitric acids, said cooling medium being out of direct contact With said reaction mixture.

5. The continuous process for the production of a liquid explosive nitric ester which comprises continuously reacting a liquid aliphatic alcohol with a nitrating acid while continuously removing the heat liberated in said reaction by maintaining said reaction mixture in direct heat exchange relationship with a single cooling medium consisting of from 50-30% nitric acid and from 30-70% sulfuric acid, said cooling medium being out of direct contact with said reaction mixture.

PHILlP G. WRIGHTSMAN. 

